Microstructural Analysis,Mechanical Behavior And Temperature Field Of TC4 Titanium Alloy And 304 Stainless Steel By Friction Stir Lap Welding

Under the general environment of�Made in China 2025�proposed to fully implement green manufacturing,improving energy efficiency ratio based on lightweight design has become a common goal in aviation,aerospace,vehicles and ships,especially the new generation of mechanical vehicles widely use titanium alloys.The research on the connection method of TC4titanium alloy(TC4)and 304 stainless steel(304 SS)has certain theoretical significance and practical application value,which replace traditional stainless steel materials.Due to the metallurgical incompatibility of 304 SS and TC4,the brittle and hard intermetallic compounds such as Ti Fe and Ti Fe₂ are easily generated at the connection interface,which will seriously reduce the joint performance.However,the use of solid-state connection technology-friction stir welding(FSW)can effectively avoid.The melting of metal can reduce the production of brittle and hard intermetallic compounds.Therefore,the reliable connection of TC4 and 304 SS using FSW technology has potential application prospects.The optimization of welding parameters of the welded joints of TC4/304 stainless steel(TC4/304 SS)by friction stir lap welding(FSLW)based on orthogonal test was researched.The results show that the higher rotational speed of the tool,the lower welding speed,resulting in the higher heat input of the joint.So under low heat input(low rotating speed and high traversing speed),there was a damaging defect at the interface without complete material flow and the minimum hardness were found at the interface,getting a minimum fracture load;under middle heat input(middle rotating speed and low traversing speed),the intermetallic compounds and the maximum hardness were discovered at the interface,and cracks started from these compounds under the tension,getting a middle fracture load;under high heat input(high rotating speed and low traversing speed),due to the high-speed rotation of the tool,the complete flow between different materials at the interface was increased,forming the mechanical�interlock�features in SZ,eventually obtaining the highest fracturing load.In addition,this paper studies the influence of different welding process parameters on the temperature field distribution of TC4/304 SS friction stir lap welding based on numerical simulation.The results show that when the rotating speed is constant,the area of the high temperature area and the peak temperature zone decrease with the increase of the traversing speed;when the traversing speed is constant,the area of the high temperature area and the peak temperature increase with the increasing rotating speed.Among them,under the condition of low heat input,the interface temperature was 912?,and the traversing speed was too fast,so that the material at the interface cannot fully react,and there was no formation of a large amount of brittle and hard intermetallic compounds;under the condition of medium heat input,the interface temperature was 930?,this temperature satisfied the temperature conditions for the formation of intermetallic compounds.Under this parameter,the rotating speed and the traversing speed were moderate,which made a large amount of brittle and hard intermetallic compounds appear at the interface;under high heat input conditions,the interface temperature was 975?,the rotating speed of the tool was too high so that a large amount of intermetallic compounds were not formed at the interface.